Comments on Step voltage 750kV lines
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Step voltage 750kV lines
Some gentlemen decided to throw a hook with wire over 750kV lines in Belarus.
They survived, however, I find in interesting to find out why. Assuming the connection to Earth was solid, there would be a large fault current and a gradient with step voltage:
According to Mike Holt in his Grounding - Safety fundamentals lecture, this is the resistance distribution around a ground pole with fault current:
In the video the guy that throws the hook is obviously within 7.6m radius, and it seems the cameramen might be as well. I understand this is an approximation, but even 1% of 750kV would be enough to end it all for them.
I would like to hear theories regarding why they got so lucky and survived. I have a few:
1.) Before the hook connected an arc formed between the live and the hook, the gap dropping most of the voltage while large current started to flow via the wire to ground, heating it up so immensely that it evaporated before a full connection to the live line could be made.
2.) This was neutral line which had some neutral-Earth voltage, (1kV?) and it was enough to evaporate the wire but not enough to cause large enough gradient for long enough to kill them
3.)The current was so high it turned the soil beneath (let's say it is sand) into glass, forming an insulator which then dropped the voltage, meanwhile the wire evaporated.
Let me know what you think happened here.
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The following users marked this post as Works for me:
| User | Comment | Date |
|---|---|---|
| Elleanor Lopez | (no comment) | Mar 18, 2024 at 18:23 |
It's really not clear what exactly happened in that video. We see someone slinging a hook over the power line, then we see a white picture. We don't know what the cable was made of and where the other end really was at the time the hook reached the power line.
One possibility is that the cable was conductive and longer than the part that ended up in the air. In other words, the bottom end of the cable was always touching the ground. It also seems likely that the guy who flung the cable released it before it touched the power line. That pretty much has to be true since it needed more slack to do that than he could provide swinging it around from his height.
Here is a likely scenario: At the moment the hook touched the power line, the person had already released the cable from his hands. Even if the cable was not insulated, it's a much larger jump from the cable to his hands than the ground, as part of the cable was lying on the ground at the time. That connection to ground would be much better than thru the air, to the person, then arcing around his boots.
If the cable was insulated with only the end stripped and touching the ground, the above would apply even more so.
Your diagram is about danger from ground currents. Those are highly unpredictable. The picture is assuming a nice uniform ground resistance, which is rarely the case. It also describes total resistance relative to a distance of 25 feet, and assumes some particular diameter rod driven into the ground.
It's not really resistance that matters, but ground potential between the two feet. You need a diagram of ground potential as a function of distance, not resistance.
Let's say the guy let go of the cable so that it's far enough not to arc to his hands. In that case the only electrical danger is the voltage offset in the ground between the two feet. If the two feet are planted the same distance from where the cable touched the ground, then there is no offset between them. Presumably the guy is wearing boots, so can actually tolerate significant ground offset under the soles.
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